The present invention is directed to a device for regulating the quantity of a pressurized fluid or paste-like medium, such as paint, lacquer, adhesive or the like, which mediums emerging from a discharge nozzle of an equipment, for example a spray gun. The device includes a feed pump having a pump chamber which receives a pump piston that is driven in oscillation. The pump chamber is connected by a suction line to a reservoir for the medium and has an outlet valve actuated by the prevailing pressure in the pump chamber for conveying the medium into a delivery chamber which is positioned before the discharge nozzle of the device.
U.S. Pat. No. 4,735,362, which claims priority from German Patent Application No. 35 29 909, and whose disclosure is incorporated by reference thereto, discloses a device having a quantitatively-controlled discharge of a medium of the above-mentioned type. In the device of this patent, the pump chamber receives a piston, which is oscillated to create a pressure in the medium contained in the chamber to force it out of an outlet valve into a delivery chamber which is connected to a discharge nozzle, which, in turn, has a second valve, which is opened by the pressure created in the delivery chamber. The second valve, whose closing element is closed by pressure of a spring, is provided in the delivery chamber to insure that the medium is discharged only if sufficient pressures prevail in the delivery chamber to obtain the desired atomization. Accordingly, the second valve is constructed so that the opening pressure is significantly higher than that of the pump outlet valve. In this device, there is also an adjustable flow control valve connected to the delivery chamber by means of which the pre-loading of the valve spring of the second valve, the stroke of the pump piston, and the paint flow can be adjusted. Thus, the medium not flowing out of the nozzle is returned to the reservoir via the flow control valve. German No. OS 16 46 190 and German No. OS 36 21 965 also disclose the regulation of the paint flow by means of valves received in return pipes.
In all of these examples of the prior art, excess medium delivered by the pump piston but not ejected through the nozzle is returned to the reservoir. Not only does this necessitate the provision of constructional measures, which require return pipes, flow restrictors, valves and the like to be incorporated in the feed pump, but often the medium, which is sometimes recirculated by the pump several times, is thereby damaged and may foam. This, in turn, will detrimentally affect the output of the pump and also will impair the spray pattern. Moreover, the measures, such as these, take direct intervention in the equipment and cannot be readily used with other equipment.